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The Photon

 Discussion between sayote and The Photon

Imported from a comment discussion on physics.stackexchange.co...
The Photon
Nov 21, 2024 19:20
Sorry, I don't know what equations you're referring to
The Photon
Nov 21, 2024 19:17
If it has a fixed charge distribution and you move the test charge near it, the distribution won't change --- that's what "fixed" means.
The Photon
Nov 21, 2024 19:16
If the charge is stated to be uniform, then it can't be a conducting plate. It must be a nonconducting region with a fixed charge distribution.
The Photon
Nov 21, 2024 19:15
(Or a photo of a page in your textbook that says that, if that's where you saw it)
The Photon
Nov 21, 2024 19:15
Can you provide a reference/link to a source that says an infinite sheet of fixed charge "blocks the field"?
The Photon
Nov 21, 2024 19:14
That said, an inifinite sheet of fixed charge would not "block the field". You'd need to sum up its effect with whatever other charges are in the system just like in your example with two fixed line charges.
The Photon
Nov 21, 2024 19:14
@sayote, your title says "infinite conducting plate", not "infinite sheet of fixed charge". I answered the question you asked. If you want to ask a different question, make a new post.
The Photon
Nov 21, 2024 19:14
Because if you add up the fields produced by the two source charges, they add up constructively. Like I said in the first paragraph, the infinite conductive sheet "blocks fields" because it contains mobile charge that can redistribute appropriately. Your two line charges don't contain mobile charge, they are fixed charges, so you shouldn't expect them to "block" the field.
The Photon
Nov 21, 2024 19:14
@sayote, for the midpoint, if you sum up the field due to the two lines (as I discussed in my 3rd paragraph) you get 0. For any point that isn't halfway between the two charged lines, that wouldn't be true. The fixed charge lines don't "block the field" everywhere between them, there just happens to be one line where their effects are equal and opposite, giving 0 net field.
 

 Discussion on question by To Jay: Var…

Imported from a comment discussion on physics.stackexchange.co...
The Photon
Nov 11, 2024 22:51
@Amit, The applied force can first work "forwards" and then work "backwards" until the object stops.
The Photon
Nov 11, 2024 22:51
And what are you asked to calculate? "Joules" could measure work done on the object, or gravitational potential energy gained by the object, or various other things. Be specific.
The Photon
Nov 11, 2024 22:51
First you said "yes" you know "acceleration as a function of time". Now you say you don't. Please update your question post with the actual and correct details of the question you want to ask.
The Photon
Nov 11, 2024 22:51
@ToJay, please edit your question post to include the information needed to answer the question.
The Photon
Nov 11, 2024 22:51
@ToJay, can you tell us more exactly what information you have. Do you know accelleration as a function of time ($a(t)$), for example? What do you mean by "NM"? New Mexico? Nanometers? Normal Mass? (If you mean newton-meters, the symbol is Nm, not NM, but then if you have the work done in newton-meters you are already done, because joules and newton-meters are the same thing)
The Photon
Nov 11, 2024 22:51
@MariusLadegårdMeyer, in English the names of people, like James Prescott Joule, are capitalized; but the names of units named after people (like joules, watts, newtons, etc.) are not capitalized. source: [NIST: "The International System of Units (SI), p. 29]. And then again the symbols for the units (J, W, N, ...) are capitalized, even though the full names of the units are not
 

 Discussion on question by zeynel: Can…

Imported from a comment discussion on physics.stackexchange.co...
The Photon
Oct 21, 2024 21:02
@zeynel, The "speed of light in a dielectric" is the result of interference between the incident light wave and light waves produced by molecules in the material that are excited by the incident wave. If we look at just the spaces between the molecules/atoms, we'll find that light is still travelling at c there. See here and here.
The Photon
Oct 21, 2024 21:02
@zeynel, if you have a different question to ask, you can simply post the new question as a new post.
The Photon
Oct 21, 2024 21:02
-1 for moving the goal-posts after answers were submitted.
The Photon
Oct 21, 2024 21:02
You're asking how to make a Star Trek transporter --- destroy the object in one place while recording its complete state of being, transmit the information to another place, and use it to reconstruct the object. I'm pretty sure that quantum mechanics makes this impossible, but that might be a philosophical question still and not 100% accepted physics.
The Photon
Oct 21, 2024 21:02
You didn't ask those questions at HN, so why did you expect them to be answered? And where did anybody say you could make the human body massless?
The Photon
Oct 21, 2024 21:02
Read the replies you got there carefully. None of them said a human body could be accelerated to the speed of light. They said 1) you can accelerate the human body as close as you want to the speed of light, but not actually achieve the speed of light. and 2) there are other massless particles besides photons, and all of them (massless particles) can (and always do) travel at the speed of light. We are not going to tell you anything different here.
 

 Discussion on question by Gurpreet Si…

Imported from a comment discussion on physics.stackexchange.co...
The Photon
Oct 18, 2024 17:20
LiNbO is used in various optical transmitter and receiver devices. Many semiconductors also have substantial electro-optic effect (but usually also high attenuation to make designing with them more difficult).
 

 Discussion on question by Falcon: Sch…

Imported from a comment discussion on travel.stackexchange.com...
The Photon
Jul 16, 2024 04:16
How did you document the status of your company? Self reporting? "Information not reliable" implies to me that they don't believe the documents you submitted are legitimate. You may need a trustworthy third party to validate the existence of your company.
 

 Discussion on question by coobit: The…

Imported from a comment discussion on physics.stackexchange.co...
The Photon
May 6, 2024 00:41
The fact that all these phenomena are similar in some ways is why we can create an analogy between them. If they didn't behave the same we couldn't treat them analogously and talk about heat flowing "down" the gradient, for example.
 

 Electrical Engineering

A place to talk with friends from the EE community about vacuu...
2
The Photon
May 4, 2024 21:57
Apparently the license was sold and they're now broadcasting in Vietnamese.
The Photon
May 4, 2024 21:57
@NickAlexeev Not this frequency but after KLIV lost their transmitter and went out of business as a news station, they maintained their license by broadcasting from a HAM station down the block from me.
The Photon
Aug 23, 2023 01:33
@rdtsc I'm kinda surprised Qorvo is getting into power solutions
The Photon
Oct 18, 2022 21:23
@adamaero HNQ can really pick some winners.
 

 Discussion on question by kehagiat: C…

Imported from a comment discussion on electronics.stackexchang...
The Photon
Apr 3, 2024 09:34
Notice that the voltage source in the book has opposite polarity from the one in the schematic you drew.
 

 Discussion on answer by Harper - Rein…

Imported from a comment discussion on travel.stackexchange.com...
The Photon
Aug 23, 2023 17:09
Do you have evidence or can cite a source showing that "Bumblebutt" communities in the US are subsidizing flights to themselves? (aside from, for example, by making use of their airports available below cost)
 

 Discussion on question by merovingian…

Imported from a comment discussion on electronics.stackexchang...
The Photon
Jun 7, 2023 12:34
Then go with my second interpretation: the "wires" on a schematic don't represent wires. They simply show connectivity of a graph. It makes no sense to talk about the potential between two points on one of these wires because each "wire" is, in the context of circuit theory actually a single point or node in the graph.
The Photon
Jun 7, 2023 12:34
You should also realize that a schematic diagram is only schematic, not physical. It indicates the connections between components in a way that clarifies the electrical function of the circuit. The "wires" drawn on the schematic don't indicate real physical separation in the physical world. Physically, they could be direct connections with no intervening wire a all.
The Photon
Jun 7, 2023 12:34
@merovingian, the theory only exists to predict how how the real circuit will behave. So if you don't understand why the theory is what it is, you need to look at the real world to see what the theory is trying to model.
The Photon
Jun 7, 2023 12:34
@merovingian circuit theory makes lots of simplifications from the complete physics of real circuits. One of them is that the resistance of connecting wires is assumed to be zero (and therefore the voltage drops across wires is taken to be zero). In the real world, the wire has a resistance, and there is a small voltage drop across it. For your own education, get the specs for a "typical wire" (whatever you think that is) and calculate how much this voltage drop is in your circuit. Then decide whether you should have neglected this in your analysis (or whether you need to buy fatter wires).
The Photon
Jun 7, 2023 12:34
Yes, it's 0/0. That's why I said math can't tell you the answer (at least, not from the limited information in the expression "0/0")
The Photon
Jun 7, 2023 12:34
You could consider that there is a small resistor r between P and Q, and take the limit of the current (considering the whole circuit design including R) as r goes to 0.
The Photon
Jun 7, 2023 12:34
You said, "If there were no potential difference, the current would be 0/R amperes," So what happens when R goes to zero also? Math can't tell you the answer.
 

 Discussion on answer by Buffy: What s…

Imported from a comment discussion on academia.stackexchange.c...
The Photon
Apr 13, 2023 06:16
@Michael_1812, I don't think OP can count on this advisor to write the positive recommendations in any case, so holding back on addressing this issue in hopes of getting them could be a lose-lose.
 

 Discussion on answer by Robert Rapple…

Imported from a comment discussion on worldbuilding.stackexcha...
The Photon
Mar 20, 2023 19:20
Clocks accurate enough (particularly when used on a ship) to determine longitude didn't exist until fairly recently. Late 18 C IIRC. So 1000's of years after the first human societies developed
 

 Discussion on answer by ACuriousMind:…

Imported from a comment discussion on physics.stackexchange.co...
The Photon
Nov 21, 2022 12:24
@JohnDoty, Gauss's law still applies to radio and even if the antenna is sensitive to field, we (at least electrical engineers do) still measure the signal strength in terms of power, so the signal strength falls off as $1/r^2$.
 

 Discussion on question by Mans: Using…

Imported from a comment discussion on physics.stackexchange.co...
The Photon
Oct 31, 2022 15:11
@FlatterMann, No, its an entirely common reason to use SPICE. But SPICE doesn't use KVL to calculate the node voltages, it uses KCL.
The Photon
Oct 31, 2022 15:11
@FlatterMann, OP asked about applying KVL, and you said you do that when you use SPICE. My point is that when you use SPICE you are applying KCL, not KVL, so you are not doing what OP asked about.
The Photon
Oct 31, 2022 15:11
@JohnDoty, but a corrolary is not the same thing as the theorem it extends.
The Photon
Oct 31, 2022 15:11
@JohnDoty but in the lumped circuit approximation we have a conservative electric field and therefore the scalar potential is uniquely defined. So you can't assume different voltage for the same node. KVL is another consequence of this, but it's not the same postulate, and we're not "using" KVL every time we use the assumption of a uniquely defined potential.
The Photon
Oct 31, 2022 15:11
@JohnDoty, given a circuit, how would you produce a set of KCL equations that leads to a solution that doesn't satisfy KVL? At what point during writing down the KCL equations do I have to do something special to "force" KVL to also be satisfied?
The Photon
Oct 31, 2022 15:11
@JohnDoty I'd say that the lumped circuit approximation is the reason KCL and KVL are valid, rather than that KVL is the reason KCL is valid.
The Photon
Oct 31, 2022 15:11
@JohnDoty, I don't see the need to "force" KVL. There are only so many independent unknowns in the circuit, so any complete independent set of linear equations describing the circuit will come up with the same solution, whether they're KCL equations, KVL equations, or a mix of the two. Of course if there's no naturally defined reference node in the circuit we have to choose one arbitrarily (at least for computer analysis) regardless of what set of equations we choose.
The Photon
Oct 31, 2022 15:11
@FlatterMann, that's fine, but OP asked about "Using KVL" and that is not what SPICE does. SPICE sets up equations based on KCL and solves those. It does not use KVL equations.
The Photon
Oct 31, 2022 15:11
@JohnDoty, Of course you get the same solution to the circuit whether you use KCL (nodal analysis) or KVL (mesh analysis). But OP is asking about "Using KVL", and that is not what SPICE does. The solutions that SPICE sets up to solve the circuit are KCL equations, not KVL equations.
The Photon
Oct 31, 2022 15:11
@FlatterMann, SPICE uses KCL (modified nodal analysis), not KVL.